Vasopressin (antidiuretic hormone, ADH) plays a major role in the regulation of blood volume, which in turn is a key, if not the predominant, factor in the long-term regulation of blood pressure. In the past several years, it has been demonstrated that the secretion of ADH from neurohypophysis is elevated in several forms of experimental and clinical hypertension. Furthermore, in some types of hypertension, ADH appears to function as a pressor agent in the maintenance of the elevated blood pressure. We propose to study the following in several different models of experimental hypertension: the effect of the orally effective converting enzyme inhibitor, SQ14, 225, on ADH secretion, and where it does have an effect, its mechanism action; the role of prostaglandins in the increased ADH secretion; pressor and renal sensitivity to ADH; and the handling of ADH by the isolated perfused rat kidney. ADH and PGE2 will be measured by radioimmunoassay.